1. Filed of the Invention
The present device relates generally to an interconnect for electronic packaging technology. More specifically, the device relates to interconnecting modules to pass millimeterwave signals.
2. Background Information
Present millimeterwave (MMW) interconnection structures are very labor intensive to construct and inspect. For larger millimeterwave systems having thousands of elements, the labor cost often becomes prohibitive for all but advanced military applications. Even with modern automated assembly equipment, the construction time is affected by the precise and complex interconnect systems used today. Precision connectors are large and costly, and use of wire bonds for jumpers is often impractical, and individual modules may not be replaced easily.
Efficient and low cost interconnection, as for example with MMIC chips, is a major challenge for successful module performance. This may be especially challenging in high frequency, large array applications. Modules tend to become quite small at higher frequencies and the connection of individual chips should preserve transmission line quality (i.e., maintain transmission line impedances and avoid discontinuities causing reflections) and should be short to minimize unnecessary time delays in processing the signals.
For example, advanced phased array applications generally dictate a very large number of antenna elements in the array to support high gain or large directivity requirements. In a typical application for extremely high frequency (EHF) 30-300 GHz antennas, a given array can include 3000-5000 elements interspersed in a periodic array. In an active aperture, array elements are associated with each of the antenna elements. The large number of antenna elements and their close spacing requires high density interconnection of the MMIC chips. For example, spacings on the order of 0.25 to 1 wavelength translate to 0.75 to 3.0 millimeters at 94 GHz.
In conventional techniques, precision hand-work is required for connecting gold ribbon, bond wire, or coaxial cables to each contact pad. In addition, free volume or space is required to accommodate wires as they are fed around the edges or over the surface of each MMIC for connection to other apparatus. An alternative is to use large diameter passages extending through the MMIC which allow for the passage of small cables or wires through the MMIC for connection to other apparatus. This consumes additional MMIC surface area and affects element spacing.
Current MMIC arrays also tend to be customized structures with variations in reliability and performance characteristics. Exact power requirements, channel cross-talk, and packaging vary from array to array. This lack of reproducibility and manufacturing consistency prevents wider application of MMIC arrays.
To transmit radiated energy between modules, several technologies are currently used. A microstrip launch with a backshort or xe2x80x9cdog housexe2x80x9d type cover can be used. The cover provides the required waveguide backshort termination and mode filter. A narrow microstrip channel formed in the microstrip substrate helps to prevent waveguide mode leakage. Since this launcher must be at least a half wavelength long, there is a limit to how small it may be.
Another technology used to transmit radiated energy is a waveguide. Waveguide connectors usually bolt together at their flanges, and generally require an inside width of at least xcex/2 to transmit a signal (where xcex is the wavelength of the signal to be transmitted). A waveguide connector requires a balun, i.e., a network for the transition from an unbalanced transmission line to a balanced transmission line, having a transition length of xcex/4. Consequently, a waveguide connector may be relatively large.
A connection to a microstrip lead, e.g., a transmitter/receiver module, can be made by transition to a stripline (e.g., press mating), a coaxial connector, or a microstrip wire bonded to another circuit. Press mating a stripline lead to another stripline generally requires a secondary soldering step to ensure adequate transmission line connectivity under any sort of vibration or temperature cycling. The performance of coaxial connectors deteriorates over time and after repeated connections due to mechanical wear. Hermetic coaxial ports used for transmitting radiated energy are generally very small. Hence, the coaxial glass seals, which themselves are difficult to assemble and bond, must be soldered to the housing wall in a time consuming, labor intensive, and costly process. Wire bonding, press mating, and use of coaxial connectors results in bulky connections that involve contact complexity. These connections, except for the coaxial connector, require connection in a plane parallel to the plane of the substrate of the radio frequency microstrip circuit. Thus, these known interconnects are unsuited for use as a millimeterwave interconnect to couple modules where the modules may have to mate to a back plane at a 90xc2x0 angle, such as in a large phased array.
U.S. Pat. No. 5,545,924 to Contolatis et al., the disclosure of which is herein incorporated by reference, provides for a three dimensional interconnect package for monolithic microwave/millimeterwave integrated circuits. However, Contolatis et al. relies upon conductor lines that are soldered together or otherwise connected, such as with wirebonding.
U.S. Pat. No. 5,235,300 to Chan et al., the disclosure of which is herein incorporated by reference, discloses packaging for millimeterwave or microwave devices. The unpackaged devices are placed in a cavity and hermetically sealed. Interconnects are then provided with a microstrip to strip line to microwave probe transition. However, the interconnects and transition are full size waveguide transitions.
U.S. Pat. No. 5.132.648 to Trihn et al., the disclosure of which is herein incorporated by reference, discloses a very large array feed-through assembly. A complex multilayer module incorporates the housing and interconnect functions for the circuit. Vias are filled with conductive metallic materials and are relied upon for signal routing and off-chip signal transfer.
U.S. Pat. No. 5,218,373 to Heckamen et al., the disclosure of which is herein incorporated by reference, discloses a device in which the propagation of signal radiation occurs through a glass window into an air dielectric waveguide. The launching of the radiation is provided by a conventional launch probe via induction through a hermetically sealed dielectric window. A periodic, waffle shaped wall structure functions to route the signal around the mounting board.
U.S. Pat. No. 5,073,761 to Waterman et al., the disclosure of which is herein incorporated by reference, discloses a non-contact interconnect in which capacitive coupling is utilized to improve the connection""s performance. Additionally, one-quarter wavelength long lines are employed in the coupling, thus dictating the minimum size of the interconnect.
The present invention is generally directed to an interconnect structure, which in accordance with exemplary embodiments, includes a first layer and a second layer for connecting an integral first signal path with a second signal path. The first layer can have a first conductor and a slot. The second layer can be positioned to be in operable communication by an opening between the first layer and the second signal path such that a distance from the first signal path to a second surface of the second layer establishes an evanescent mode of signal propagation. The evanescent mode is only required to propagate a very short distance, and thus introduces negligible attenuation and reflection.
The interconnect structure provides a rugged, compact interconnect that can be configured substantially smaller than a waveguide, compatible with existing MMIC assembly methods, repeatedly and easily connected and disconnected, and can allow easy test fixturing for modules.